U.S. Pat. No. 3,185,297 shows a surface covering or building wall material which includes a semi-hydrated gypsum. A strip of such material is typically applied to a wall or other substrate by spraying or coating sufficient water to a sheet of the material to hydrate the gypsum and cause it to set and harden. While this material can be adequately applied by a skilled worker, the novice or amateur worker frequently has difficulty in gauging the appropriate quantity of water which should be added. Typically, the novice adds a large excess of water which will run into the floor and otherwise create a mess. The extra water causes the gypsum to sag and displace.